Relationships between wild bee abundance and fruit set of Camellia oleifera Abel

Camellia oleifera Abel. is an economically important plant for edible oils. To investigate the importance of wild bee abundance at different canopy and spatial scale for fruit set of Camellia oleifera, we evaluated the relationship of bee abundance with fruit set using yellow pan trap, with additional focus on distance and wild bee abundance counts at a farm in China for 2 years. We found that yellow traps collected 95% more individual bees than the second-best (pink) trap colour. Looking across canopy positions, the number of wild bees (including Colletes gigas, Andrena camellia, Andrena striata, Andrena hunanensis and Andrena chekiangensis) varied significantly in each year. The fruit set also varied significantly based on canopy position. In 2018, there was with an average fruit set of 34.13% in the lower canopy, 54.30% in the middle canopy and 47.41% in the upper canopy. In 2019, fruit set was 29.67% in the lower canopy, 54.15% in the middle canopy and 47.36% in the upper canopy. Comparing inter-annual changes, only the fruit set and number of bees in the low canopy showed significant differences between 2018 and 2019. Fruit set and wild bee abundance were positively correlated in all canopy layers in each year, and there was an interactive effect between canopy and bee abundance on fruit set. Across 205 trees, growth indicators, crown size and tree height, increased significantly from 2018 to 2019, but the fruit set did not increase with the significant increase in the number of flowers. From the spatial perspective, wild bee abundance and fruit set were positively correlated, but fruit set was negatively correlated with distance from a large bee nesting aggregation nearby. Among the variables investigated, bee abundance seems to have the strongest influence on fruit set in C. oleifera.     

Orchard pollination in Capitol Reef National Park,Utah, USA. Honey bees or native bees?

Capitol Reef National Park in central Utah, USA surrounds 22 managed fruit orchards started over a century ago by Mormon pioneers. Honey bees are imported for pollination, although the area in which the Park is embedded has over 700 species of native bees, many of which are potential orchard pollinators. We studied the visitation of native bees to apple, pear, apricot, and sweet cherry over 2 years. Thirty species of bees visited the flowers but, except for pear flowers, most were uncommon compared to honey bees. Evidence that honey bees prevented native bees from foraging on orchard crop flowers was equivocal: generally, honey bee and native bee visitation rates to the flowers were not negatively correlated, nor were native bee visitation rates positively correlated with distance of orchards from honey bee hives. Conversely, competition was tentatively suggested by much larger numbers of honey bees than natives on the flowers of apples, apricots and cherry; and by the large increase of native bees on pears, where honey bee numbers were low. At least one-third of the native bee species visiting the flowers are potential pollinators, including cavity-nesting species such as Osmia lignaria propinqua, currently managed for small orchard pollination in the US, plus several fossorial species, including one rosaceous flower specialist (Andrena milwaukiensis). We suggest that gradual withdrawal of honey bees from the Park would help conserve native bee populations without decreasing orchard crop productivity, and would serve as a demonstration of the commercial value of native pollinators.     

Small local population sizes and high habitat patch fidelity in a specialised solitary bee

Andrena hattorfiana is a rare solitary bee which has declined during the last decades throughout western Europe. It is specialised to forage pollen from plants of the family Dipsacaceae. Knowledge of distribution, dispersal propensity, and local population sizes is essential for successful conservation of A. hattorfiana. The investigated local bee populations (n = 78) were dominated by small local populations and 60% were smaller than 10 female individuals and 80% were smaller than 50 female individuals. The area of the median occupied habitat patch was 1.25 hectare and harboured 7 female bees. Mark-release-recapture studies of female A. hattorfiana revealed a sedentary behaviour. Among pollen-foraging female bees the average registered distance moved was 46 m. The patch emigration rate was about 2%, with an observed maximum colonization distance of 900 m. Only 10% of the individuals crossed areas without the pollen plant within grassland patches, such as unpaved roads, stone walls and small tree-stands, even if these areas were less than 10 m wide. This study shows that solitary bees can occur in local populations of extremely small size and they have a sedentary behaviour. These are features that usually increase the risk of local population extinction.     

Sex pheromone mimicry in the early spider orchid (Ophrys sphegodes): patterns of hydrocarbons as the key mechanism for pollination by sexual deception

We investigated the female-produced sex pheromone of the solitary bee Andrena nigroaenea and compared it with floral scent of the sexually deceptive orchid Ophrys sphegodes which is pollinated by Andrena nigroaenea males. We identified physiologically and behaviorally active compounds by gas chromatography with electroantennographic detection, gas chromatography-mass spectrometry, and behavioral tests in the field. Dummies scented with cuticle extracts of virgin females or of O.sphegodes labellum extracts elicited significantly more male reactions than odorless dummies. Therefore, copulation behavior eliciting semiochemicals are located on the surface of the females' cuticle and the surface of the flowers. Within bee and orchid samples, n-alkanes and n-alkenes, aldehydes, esters, all-trans-farnesol and all-trans-farnesyl hexanoate triggered electroantennographic responses in male antennae. Most of the alkanes and alkenes occurred in similar patterns both in the bees and orchids. O. sphegodes leaf extracts contained mostly the same compounds but in different proportions. In behavioral tests with synthetic compounds, blends of alkenes triggered significantly more approaches and pounces of the males whereas alkanes were not more attractive than odorless dummies. Since alkanes and alkenes together were most attractive, we conclude they constitute the bees' sex pheromone as well as the pseudocopulation-behavior releasing orchid-odor bouquet. Accepted: 30 March 2000     

Reproduction of <Emphasis Type="Italic">Amorpha canescens</Emphasis> (Fabaceae) and diversity of its bee community in a fragmented landscape

Loss of insect pollinators due to habitat fragmentation often results in negative effects on plant reproduction, but few studies have simultaneously examined variation in the bee community, site characteristics and plant community characteristics to evaluate their relative effects on plant reproduction in a fragmented habitat. We examined the reproduction of a common tallgrass prairie forb, Amorpha canescens (Fabaceae), in large (>40 ha) and small (<2 ha) prairie remnants in Iowa and Minnesota in relation to the diversity and abundance of its bee visitors, plant population size, and species density of the forb flowering community. We found significant positive effects of the diversity of bees visiting A. canescens on percent fruit set at a site in both years of the study and in 2002 an additional significant positive effect of plant species density. Abundance of bees visiting A. canescens had a significant positive effect on percent fruit set in 2002, but was only marginally significant in 2003. In 2003 but not 2002, the plant species density at the sites had a significant negative effect on the diversity and abundance of bees visiting A. canescens, indicating community-level characteristics can influence the bee community visiting any one species. Site size, a common predictor of plant reproduction in fragmented habitats did not contribute to any models of fruit set and was only marginally related to bee diversity one year. Andrena quintilis, one of the three oligolectic bee species associated with A. canescens, was abundant at all sites, suggesting it has not been significantly affected by fragmentation. Our results show that the diversity of bees visiting A. canescens is important for maintaining fruit set and that bee visitation is still sufficient for at least some fruit set in all populations, suggesting these small remnants act as floral resource oases for bees in landscapes often dominated by agriculture.     

Solitary invasive orchid bee outperforms co-occurring native bees to promote fruit set of an invasive Solanum

Our understanding of the effects of introduced invasive pollinators on plants has been exclusively drawn from studies on introduced social bees. One might expect, however, that the impacts of introduced solitary bees, with much lower population densities and fewer foragers, would be small. Yet little is known about the potential effects of naturalized solitary bees on the environment. We took advantage of the recent naturalization of an orchid bee, Euglossa viridissima, in southern Florida to study the effects of this solitary bee on reproduction of Solanum torvum, an invasive shrub. Flowers of S. torvum require specialized buzz pollination. Through timed floral visitor watches and two pollination treatments (control and pollen supplementation) at three forest edge and three open area sites, we found that the fruit set of S. torvum was pollen limited at the open sites where the native bees dominate, but was not pollen limited at the forest sites where the invasive orchid bees dominate. The orchid bee’s pollination efficiency was nearly double that of the native halictid bees, and was also slightly higher than that of the native carpenter bee. Experiments using small and large mesh cages (to deny or allow E. viridissima access, respectively) at one forest site indicated that when the orchid bee was excluded, the flowers set one-quarter as many fruit as when the bee was allowed access. The orchid bee was the most important pollinator of the weed at the forest sites, which could pose additional challenges to the management of this weed in the fragmented, endangered tropical hardwood forests in the region. This specialized invasive mutualism may promote populations of both the orchid bee and this noxious weed. Invasive solitary bees, particularly species that are specialized pollinators, appear to have more importance than has previously been recognized. Electronic supplementary material  The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

Solitary and group nesting in the orchid bee <Emphasis Type="Italic">Euglossa hyacinthina</Emphasis> (Hymenoptera,Apidae)

Summary Orchid bees (Euglossini) provide a potentially informative contrast for examining origins of advanced social behaviour in bees because they are the only tribe in the apine clade that do not form large colonies or have queens and workers. We investigated natural nests of Euglossa hyacinthina Dressler, an orchid bee that nests singly or in groups. By comparing the two types of nests, we examined if individuals in a group merely share the nest (are communal) or exhibit a level of social organization where there is reproductive division of labour among the females. Observations are consistent with communal nesting, indicating that all females in group nests are reproductively similar to the solitary nesting females because the provisioning of young, as well as the ovary development and mating status of females sharing nests were not different than that of solitary-nesting females. Also, multiple female nests did not produce a female-biased brood as predicted for nests with reproductive division of labour. We also investigated potential advantages of group nesting vs. individual nesting. We demonstrate that per capita offspring production is lower in nests with more than one female. However, we found that nests with single females were left unattended for longer periods of time during foraging, and that there was a high incidence of natural enemy attack in nests when females were absent. Group and solitary nesting may be advantageous under different conditions.Received 3 December 2002; revised 7 March 2003; accepted 2 April 2003.     

Division of Labor Associated with Brood Rearing in the Honey Bee: How Does It Translate to Colony Fitness?

Division of labor is a striking feature observed in honey bees and many other social insects. Division of labor has been claimed to benefit fitness. In honey bees, the adult work force may be viewed as divided between non-foraging hive bees that rear brood and maintain the nest, and foragers that collect food outside the nest. Honey bee brood pheromone is a larval pheromone that serves as an excellent empirical tool to manipulate foraging behaviors and thus division of labor in the honey bee. Here we use two different doses of brood pheromone to alter the foraging stimulus environment, thus changing demographics of colony division of labor, to demonstrate how division of labor associated with brood rearing affects colony growth rate. We examine the effects of these different doses of brood pheromone on individual foraging ontogeny and specialization, colony level foraging behavior, and individual glandular protein synthesis. Low brood pheromone treatment colonies exhibited significantly higher foraging population, decreased age of first foraging and greater foraging effort, resulting in greater colony growth compared to other treatments. This study demonstrates how division of labor associated with brood rearing affects honey bee colony growth rate, a token of fitness.     

Biology of <Emphasis Type="Italic">Lasioglossum</Emphasis> (<Emphasis Type="Italic">L.</Emphasis>) <Emphasis Type="Italic">majus</Emphasis> (Hymenoptera: Halictidae), a largely solitary sweat bee with behavioural adaptations to communality

Within the bee family Halictidae there have been three origins of sociality. Although detection of origins and reversal from sociality requires phylogenetic studies, at a behavioural level a predisposition to sociality can be detected by analysis of intra-specific interactions. We studied aspects of nesting biology and behavioural interactions in Lasioglossum (Lasioglossum) majus, a poorly known halictine inhabiting temperate regions of Europe, which is suspected to be solitary. Nests were found to be largely used by one female, but some were shared by more than one individual. These few nests, whose entrances were very close to each other, were found to be connected underground. A few individuals were observed to enter in a nest where a female was waiting, behaving as a guard and allowing the incoming bee to enter the nest. By use of circle-tube experiments, the behavioural repertoire exhibited by females during encounters was assessed. Levels of withdrawal and cooperative events were comparable with those observed in other solitary nesting species, but aggressive events were very rare, as in several observed communal species. We conclude that L. (L.) majus females, despite general solitary nesting, possess behavioural components enabling them to adopt, probably in high nest-density areas, nest-sharing strategies. A similar kind of local social polymorphism has been observed in two other species of the subgenus Lasioglossum, but these are the first data available on a European species and the first record of subterranean connections among nests of halictid bees.     

Effects of familiarity and nestmate number on social interactions in two communal bees, Andrena scotica and Panurgus calcaratus (Hymenoptera, Andrenidae)

Summary: Communality is considered a widespread form of social organization in bees and wasps, one in which two or more females of the same generation share a common nest and amongst whom there is no reproductive division of labor. The evolution and maintenance of egalitarian communal societies poses theoretical difficulties where 'cheating' amongst nestmates is practised. Yet there is little knowledge of the intranidal social interactions among communal conspecifics that allow an understanding of the degree of cooperation versus exploitation amongst nestmates in such societies. Using a circle-tube arena, we staged interactions in the laboratory among pairs of female conspecifics using two communal andrenid species, Andrena scotica and Panurgus calcaratus, to score their cooperative and aggressive behaviors. For both species, females did not discriminate between familiar (nestmate) and unfamiliar (non-nestmate) conspecifics in their cooperative and aggressive behaviors, suggesting that there is universal acceptance of conspecifics. Levels of cooperation and aggression did not vary with the number of nestmates in the nest of origin for either species. In addition, frequencies of social interactions did not vary with body size, wing wear or ovarian development in P. calcaratus. Interspecific comparisons were made with published data on social interactions of other bee species at varying levels of social organization (solitary to eusocial) derived from analogous circle-tube experiments. Panurgus calcaratus displayed highly cooperative behavior, similar to that of a previously studied communal bee, Lasioglossum hemichalceum (Kukuk, 1992a). Andrena scotica displayed lower levels of cooperation, and was in this sense more similar to solitary species and to interactions amongst non-nestmate individuals of eusocial species. Both A. scotica and P. calcaratus displayed very low levels of aggressive behavior, again similar to L. hemichalceum. As a working hypothesis, we suggest the existence of a communal behavioral syndrome comprising high levels of intranidal cooperation and low aggression, both directed indiscriminately at conspecifics.     

Male-biased sex ratio and promiscuous pollination in the dioecious island treeLaurus azorica (Lauraceae)

Pollination ofLaurus azorica (Lauraceae), a dioecious Macaronesian tree, was studied. Male and female trees had the same size distribution. The population had 2.5 times as many male trees as females. In addition, males produced more flowers, and their inflorescences lasted longer. Individual flower lifetime and length of flowering season were the same in both sexes. Between the years of observation, one tree changed sex. Pollinators wereHalictinae bees and the flyTachina canariensis. The bees collected pollen and nectar and the fly collected nectar from both sexes. Both species visited other plants as well. The evolution of breeding systems inLauraceae is discussed.     

Co-dependency between a specialist <Emphasis Type="Italic">Andrena</Emphasis> bee and its death camas host, <Emphasis Type="Italic">Toxicoscordion paniculatum</Emphasis>

Among associations of plants and their pollinating bees, mutually specialized pairings are rare. Typically, either pollen specialist (oligolectic) bees are joined by polylectic bees in a flowering species’ pollinator guild, or specialized flowers are pollinated by one or more polylectic bees. The bee Andrena astragali is a narrow oligolege, collecting pollen solely from two nearly identical species of death camas (Toxicoscordion, formerly Zigadenus). Neurotoxic alkaloids of these plants are implicated in sheep and honey bee poisoning. In this study, T. paniculatum, T. venenosum and co-flowering forbs were sampled for bees at 15 sites along a 900-km-long east–west transect across the northern Great Basin plus an altitudinal gradient in northern Utah’s Bear River Range. Only A. astragali bees were regularly seen visiting flowering panicles of these Toxicoscordion. In turn, this bee was never among the 170 bee species caught at 17 species of other prevalent co-occurring wildflowers in the same five state region (38,000 plants surveyed). Our field pollination experiments show that T. paniculatum is primarily an outcrosser dependent on pollinator visitation for most capsule and seed set. Thus, both A. astragali and two sister species of Toxicoscordion are narrowly specialized and co-dependent on each other for reproduction, illustrating a rare case of obligate mutual specialization in bee–plant interactions.     

Generalized host‐plant feeding can hide sterol‐specialized foraging behaviors in bee–plant interactions

Host‐plant selection is a key factor driving the ecology and evolution of insects. While the majority of phytophagous insects is highly host specific, generalist behavior is quite widespread among bees and presumably involves physiological adaptations that remain largely unexplored. However, floral visitation patterns suggest that generalist bees do not forage randomly on all available resources. While resource availability and accessibility as well as nectar composition have been widely explored, pollen chemistry could also have an impact on the range of suitable host‐plants. This study focuses on particular pollen nutrients that cannot be synthesized de novo by insects but are key compounds of cell membranes and the precursor for molting process: the sterols. We compared the sterol composition of pollen from the main host‐plants of three generalist bees: Anthophora plumipes, Colletes cunicularius, and Osmia cornuta, as well as one specialist bee Andrena vaga. We also analyzed the sterols of their brood cell provisions, the tissues of larvae and nonemerged females to determine which sterols are used by the different species. Our results show that sterols are not used accordingly to foraging strategy: Both the specialist species A. vaga and the generalist species C. cunicularius might metabolize a rare C₂₇ sterol, while the two generalist species A. plumipes and O. cornuta might rather use a very common C₂₈ sterol. Our results suggest that shared sterolic compounds among plant species could facilitate the exploitation of multiple host‐plants by A. plumipes and O. cornuta whereas the generalist C. cunicularius might be more constrained due to its physiological requirements of a more uncommon dietary sterol. Our findings suggest that a bee displaying a generalist foraging behavior may sometimes hide a sterol‐specialized species. This evidence challenges the hypothesis that all generalist free‐living bee species are all able to develop on a wide range of different pollen types.     

Intranidal mating,emergence, and sex ratio in a communal beeAndrena jacobi Perkins 1921 (Hymenoptera: Andrenidae)

The extent of preemergence intranidal mating, schedules of emergence, and sex ratio at emergence were documented forAndrena jacobi, a communal, univoltine bee, by collecting and dissecting adults as they emerged from their fossorial nests in 1994. Over 70% of females had mated intranidally with nestmate males, thus potentially incestuously, before emerging. Preemergence intranidal mating did not vary during a day or between nests within a day, though it was less frequent at the start and end of the period of emergence. It was independent of a female's size.A. jacobi was protandrous, though some males emerged after all females. The sex ratio at emergence was remarkably female biased, possibly a consequence of local mate competition. Intranidal mating may represent a characteristic trait of communal bees where a high density of receptive females are predictably aggregated within a nest.     

Records of bees (Hymenoptera: Apoidea) new to both Georgia and Transcaucasia revealed by DNA barcoding

Community composition of local pollinator assemblages, population dynamics and distribution patterns of many species are still poorly known, especially in little studied regions like Transcaucasia. We generated a total of 189 DNA barcodes from bees collected in 14 apple orchards in central and eastern Georgia to extend our knowledge of their distribution. Sequences (ca. 700 bp of the mitochondrial cytochrome oxidase I gene) were compared to the NCBI nucleotide database. Using a threshold of 98% similarity, analyses suggested that the sampled bees belong to 36 species of Apidae, Andrenidae, Halictidae, and Megachilidae. We report five bee species for the first time for Georgia: Andrena alfkenella Perkins, 1914, Halictus cochlearitarsis Dours, 1871, Nomada goodeniana (Kirby, 1802), Nomada ruficornis (Linnaeus, 1758) and Eucera nigrescens Pérez, 1879, four of which are also new for the Transcaucasia region. With these additions, the number of bee species known to occur in Georgia increases to 371.     

Recognition of scent marks in solitary bees to avoid previously visited flowers

Knowing how floral visitors forage efficiently among flowers is important to understanding plant-pollinator interactions. When bees search for rewarding flowers, they use several visual cues to detect the available floral resources. In addition to these cues, bees can recognize scent marks, which are olfactory cues left on flowers foraged by previous visitors. This behavior is well known in social bees, such as honeybees and bumblebees. Although solitary bees do not need to give information about which flowers were foraged to conspecifics, several pieces of evidence have indicated the use of scent marks. However, it is unknown whether the behavior is widely used in many different bee species. We investigated whether four different solitary bees, Colletes patellatus (Colletidae), Andrena prostomias (Andrenidae), Osmia orientalis (Megachilidae), and Tetralonia mitsukurii (Apidae), can recognize flowers that have been foraged previously by visitors within 3 min. All four bees showed rejection responses to flowers foraged by conspecifics. However, our results showed that responses to foraged flowers varied among bee species. The tendency of A. prostomias and T. mitsukurii to reject the foraged flowers was pronounced, while in C. patellatus and O. orientalis it was weak. In both A. prostomias and T. mitsukurii, the rejection rate of flowers foraged by conspecifics decreased as the time lag after the last visit increased. Both bees visited the flowers from which pollen or nectar had been artificially removed. We suggest that A. prostomias and T. mitsukurii would recognize scent marks left by previous visitors, while the other two bees would not recognize them so strongly. It is likely that the decision to use scent marks is dependent either on the richness of resources or on the complexity of floral structure.     

Pollination of Campanula rapunculus L. (Campanulaceae): How much pollen flows into pollination and into reproduction of oligolectic pollinators?

We studied an isolated population of Campanula rapunculus and two oligolectic bee species of Chelostoma (Megachilidae), their main pollinators. The population of C. rapunculus consisted of 2808 plants. Measurements of pollen flow showed that 3.7% of the pollen produced by a flower contribute to pollination, 95.5% was collected by bees for their offspring and 0.8% remained on the styles. Pollen analyses of brood cells of Chelostoma rapunculi revealed that females collected on average 4.9 million Campanula pollen to rear one bee. We calculated that approximately 1588 bees of this species could have been reared at the study site during the studied season. The amount of potentially viable pollen deposited on stigmas was 3.6 to 10.7 times higher than the number of ovules. We discuss morphological features of the flowers which may lower the pollen removal rate per bee visit and consequently cause a high visitation and pollination rate.The study was supported by a joint project CAPES / DAAD (Probral 112/00). We thank NaBu (Naturschutzbund) Bonn and the Untere Landschaftsbehörde Siegburg for the permission to work at the Natural Reserve Dünstekoven.     

PCR-based detection of a tracheal mite of the honey bee Acarapis woodi

The effects of the tracheal mite Acarapis woodi on the health of honey bees have been neglected since the prevalence of Varroa mites to Apis mellifera colonies. However, tracheal mite infestation of honey bee colonies still occurs worldwide and could impose negative impact on apiculture. The detection of A. woodi requires the dissection of honey bees followed by microscopic observation of the tracheal sacs. We thus developed PCR methods to detect A. woodi. These methods facilitate rapid and sensitive detection of A. woodi in many honey bee samples for epidemiologic surveys.     

Negative correlation between Nosema ceranae spore loads and deformed wing virus infection levels in adult honey bee workers

Interactions between pathogens might contribute to honey bee colony losses. Here we investigated if there is an association between the microsporidian Nosema ceranae and the deformed wing virus (DWV) in different body sections of individual honey bee workers (Apis mellifera ligustica) under exclusion of the vector Varroa destructor. Our data provide correlational evidence for antagonistic interactions between the two pathogens in the midgut of the bees.